The present disclosure relates to orthopedics devices and, more particularly, to knee prostheses.
During articulation of a natural knee joint, flexion between the tibia and the femur takes place about a transverse axis while some relative rotation between the tibia and the femur occurs about a longitudinal axis. Such flexion and rotation is necessary to carry out a normal gate cycle. It has been established that in full extension the tibia is rotationally displaced, relative to the femur, by approximately 2-3 degrees. As the natural knee flexes, the tibia rotates internally. According to previous studies, about 5 degree of rotation ordinarily occurs as the knee is articulated from 0 degree to 10 degree of flexion; thereafter, little further rotation occurs up to at least about 45 degree of flexion. Total rotation at 110 degrees of flexion is approximately 20 degrees.
Rotational stability of the natural knee is provided by the collateral and cruciate ligaments. The cruciate ligaments deter uncontrolled internal rotation within a certain range of flexion of the knee, while the collateral ligaments provide transverse stability and deter uncontrolled external rotation of the tibia. Where the natural knee is replaced by a total knee prosthesis, either the anterior cruciate ligament or both the anterior and posterior cruciate ligaments ordinarily are sacrificed. In the instances where the knee prosthesis is constrained to supply the stability ordinarily provided by the sacrificed ligaments, it is desirable for the knee prosthesis to mimic the natural knee as closely as possible.
Although several knee prostheses have been developed over the years, improvements are still possible. A need exists for knee prostheses capable of more closely imitating the natural knee.
As used herein, when referring to bones or other parts of the body, the term “proximal” means closer to the heart and the term “distal” means more distant from the heart. The term “inferior” means towards the feet and the term “superior” means towards the head. The term “anterior” means towards the front part of the body or the face and the term “posterior” means towards the back of the body. The term “medial” means towards the midline of the body and the term “lateral” means away from the midline of the body.